Continuous production process of high-strength and high-modulus polyolefin material

Abstract

A high-strength and high-modulus polyolefin material can be continuously produced from a polyolefin in a powder form by feeding the polyolefin powder between a combination of endless belts disposed in an up-and-down opposing relation, compression-molding the polyolefin powder at a temperature lower than the melting point of the polyolefin powder by means of a pressing device while holding the polyolefin powder between the endless belts and conveying the same, and then rolling and stretching the resultant compression-molded polyolefin. The pressing device is constructed of pressing platens and corresponding sets of rollers, which are all accommodated within the respective endless belts. The rollers in each set are connected together, and the sets of rollers are arranged movably in an endless fashion between the respective platens and the endless belts associated therewith.

We claim: 
     
       1. A process for the continuous production of a high-strength and high-modulus polyolefin material, which comprises: feeding a polyolefin in a powder form between a combination of endless belts disposed in an up-and-down opposing relation;   compression-molding the polyolefin powder at a temperature lower than the melting point of the polyolefin powder by means of a pressing means while holding the polyolefin powder between the endless belts and conveying the same, said pressing means comprising pressing platens and corresponding sets of rollers, all accommodated within the respective endless belts, the rollers in each set being connected together, and said sets of rollers being arranged movably in an endless fashion between the respective platens and the endless belts associated therewith; and   rolling the resultant compression-molded polyolefin, followed by stretching.   
     
     
       2. The process of claim 1, wherein the polyolefin is selected from the group consisting of homopolymers of α-olefins having 2-8 carbon atoms, copolymers of ethylene and α-olefins having 3-12 carbon atoms and copolymers of propylene and α-olefins having 4-12 carbon atoms. 
     
     
       3. The process of claim 2, wherein the polyolefin has a particle size distribution in a range of 10-2,000 μm. 
     
     
       4. The process of claim 1, wherein the endless belts have a belt thickness of 0.1-1.5 mm and a surface polished in a mirror-finished state. 
     
     
       5. The process of claim 4, wherein the rollers have an outer diameter of 5-30 mm. 
     
     
       6. The process of claim 1, wherein the endless belts have a running length of 30-400 cm and the press platens an average pressure of 0.1-20 kg/cm 2  to the endless belts. 
     
     
       7. The process of claim 2, wherein the compression-molding step is performed at 50° C. or higher where the polyolefin is a polyethylene polymer and at 90° C. or higher where the polyolefin is a polypropylene polymer. 
     
     
       8. The process of claim 2, wherein the temperature for the compression-molding step is maintained by a preheater provided in the proximity of at least one of the endless belts and a heating means applied to at least one of the press platen. 
     
     
       9. The process of claim 1, wherein the endless belts are driven at a running speed of 30-400 cm/min. 
     
     
       10. The process of claim 1, wherein the pressing means is fed with a pressure from at least one hydraulic cylinder. 
     
     
       11. The process of claim 1, wherein the compression-molded polyolefin is rolled at a deformation ratio of 1.2-20 in terms of rolling efficiency. 
     
     
       12. The process of claim 11, wherein the rolling step is performed at a rolling temperature in a range of at least 20° C. but lower than the melting point of the polyolefin powder. 
     
     
       13. The process of claim 1, wherein the thus-rolled polyolefin is stretched by pulling the same in accordance with a method selected from the group consisting of hot-air stretching, cylinder stretching, roll stretching and hot-platen stretching. 
     
     
       14. The process of claim 13, wherein the stretching is performed in a temperature range of 20°-150° C. 
     
     
       15. The process of claim 14, wherein the stretching is performed in multiple steps and the stretching in a latter step is conducted at a higher temperature than in the preceding step. 
     
     
       16. The process of claim 1, wherein the stretching is performed in a speed range of 0.1-200 m/min. 
     
     
       17. The process of claim 2, wherein the polyolefin is an ultra-high-molecular-weight polyethylene and the stretching is performed at a draw ratio of at least 60-fold. 
     
     
       18. A process for the continuous production of a high-strength and high-modulus polyolefin material, which comprises: feeding a polyolefin in a powder form between a combination of endless belts disposed in an up-and-down opposing relation;   compression-molding the polyolefin powder at a temperature lower than the melting point of the polyolefin powder by means of a pressing means while holding the polyolefin powder between the endless belts and conveying the same, said pressing means comprising pressing platens and corresponding sets of rollers, all accommodated within the respective endless belts, the rollers in each set being connected together, and said sets of rollers being arranged movably in an endless fashion between the respective platens and the endless belts associated therewith, wherein the temperature for the compression-molding step is maintained by heating means applied to at least one of the press platen; and   rolling the resultant compression-molded polyolefin, followed by stretching.   
     
     
       19. The process of claim 18, wherein the stretching is performed in multiple steps. 
     
     
       20. The process of claim 18, wherein the stretching in a later step is conducted at a higher temperature than in the preceding step. 
     
     
       21. The process of claim 18, wherein the temperature for the compression-molding step is maintained by a preheater provided in the proximity of at least one of the endless belts. 
     
     
       22. The process of claim 18, wherein the polyolefin is selected from the group consisting of homopolymers of α-olefins having 2-8 carbon atoms, copolymers of ethylene and α-olefins having 3-12 carbon atoms and copolymers of propylene and α-olefins having 2-12 carbon atoms. 
     
     
       23. The process of claim 22, wherein the polyolefin has a particle size distribution in a range of 10-2,000 μm. 
     
     
       24. The process of claim 18, wherein the endless belts have a belt thickness of 0.1-1.5 mm and a surface polished in a mirror-finished state. 
     
     
       25. The process of claim 24, wherein the rollers have an outer diameter of 5-30 mm. 
     
     
       26. The process of claim 18, wherein the endless belts have a running length of 30-400 cm and the press platens apply an average pressure of 0.1-20 kg/cm 2  to the endless belts. 
     
     
       27. The process of claim 24, wherein the compression-molding step is performed at 50° C. or higher where the polyolefin is a polyethylene polymer and at 90° C. or higher where the polyolefin is a polypropylene polymer. 
     
     
       28. The process of claim 18, wherein the endless belts are driven at a running speed of 30-400 cm/min. 
     
     
       29. The process of claim 18, wherein the pressing means is fed with a pressure from at least one hydraulic cylinder. 
     
     
       30. The process of claim 18, wherein the compression-molded polyolefin is rolled at a deformation ratio of 1.2-20 in terms of rolling efficiency. 
     
     
       31. The process of claim 30, wherein the rolling step is performed at a rolling temperature in a range of at least 20° C. but lower than the melting point of the polyolefin powder. 
     
     
       32. The process of claim 18, wherein the thus-rolled polyolefin is stretched by pulling the same in accordance with a method selected from the group consisting of hot-air stretching, cylinder stretching, roll stretching and hot-platen stretching. 
     
     
       33. The process of claim 32, wherein the stretching is performed in a temperature range of 20°-150° C. 
     
     
       34. The process of claim 33, wherein the stretching is performed in multiple steps and the stretching in a latter step is conducted at a higher temperature than in the preceding step. 
     
     
       35. The process of claim 18, wherein the stretching is performed in a speed range of 0.1-200 m/min. 
     
     
       36. The process of claim 22, wherein the polyolefin is an ultra-high-molecular-weight polyethylene and the stretching is performed at a draw ratio of at least 60-fold.